The present invention relates to a data transmission system and a data transmission and receiving apparatus, more particularly to a data receiving apparatus, a data transmission system, and a data transmission method therefor which relate to broadcasting and communication of digitized sound and image data and other data information, which receive data by a simple receiving method stressing real time and low power consumption at the time of BGM or free distribution and broadcasting, which allow highly reliable data reception at the time of storing received data or pay distribution and broadcasting, and which otherwise enable control of data reliability and receiving cost according to the mode of reception and which establish a charging system for distribution and broadcasting.
In the field of data transmission, especially in digital broadcasting, a transmission side encodes image, sound, and other source data, multiplexes the encoded data, applies channel encoding, and sends the data through an antenna or a transmission line. A receiving side basically applies processing reverse to that performed at the transmission side to reproduce the original data forming the source. In other words, it performs channel decoding, demultiplexing, and source decoding.
FIG. 5 shows an example of the configuration of a basic data transmission system. Here, the explanation is given assuming two kinds of sources. In FIG. 5, 5 and 6 are source data. Note that these source data include, for example, sound data, image data, composite data corresponding to a composite signal including both sound and image signals such as a TV signal, and computer information data such as software and databases handled by computers.
In FIG. 5, 10 and 11 are information-data generation circuits for performing predetermined processing on the source data 5 and 6, while 12 and 13 are information data generated by the information-data generation circuits 10 and 11. Reference numeral 14 shows a multiplexing circuit. The multiplexing circuit 14 multiplexes the information data 12 and 13 by a predetermined method to obtain the multiplexed data 15. Reference numeral 16 is a channel encoding circuit comprised of an encoding circuit 29 and a modulation circuit 30. The encoding circuit 29 performs error-correcting coding by a predetermined method. The modulation circuit 30 performs digital modulation by a predetermined method. Reference numeral 17 is channel-encoded data (hereinafter called transmission data). Reference numeral 18 is a transmission line. Here, the transmission line 18 is, for example, an electromagnetic wave.
In the transmission line 18, noise 28 is added to the transmission signal 17 from a noise source 27. Reference numeral 19 is a transmission signal to which noise is added. This becomes the signal input to a receiving apparatus. Reference numeral 20 is a channel decoding circuit comprised of a digital demodulator 31 and an error-correcting decoder 32. The digital demodulator 31 performs digital demodulation by a predetermined method. The error-correcting decoder 32 performs error-correcting decoding by a predetermined method. Reference numeral 21 is a channel-decoded result, while 22 is a demultiplexer. The demultiplexer 22 demultiplexes the data by a predetermined method. Reference numeral 23 is demultiplexed data corresponding to the information data 12, while 25 is an source reproduction circuit. Reference numeral 24 is demultiplexed data corresponding to the information data 13, while 26 is an source reproduction circuit. Source-reproduced data 33 and 34 are viewed and listened to in real time or stored in a storage medium such as tape or a disk. Data to be transmitted is shown in FIG. 6. Here, the data to be transmitted is, for example, a TS (transport stream) of MPEG-2 Systems (ITU-TH, 222, 0, ISO/IEC 13818-1). In this case, 12 and 13 shown in FIG. 5 are TS""s of information data corresponding to the source data 5 and 6, respectively. The output of the multiplexing circuit 14, that is, the multiplexed data 15, is a TS comprised of the information data 12 and 13 multiplexed.
A TS is comprised of TSP""s (transport stream packets). A TSP, as shown in FIG. 6, is a fixed-length packet comprised of a total of 188 bytes including a synchronization byte (Oxc3x9747), a TS header (four bytes including the synchronization byte), and a data section of 184 bytes. The TS header includes a packet identifier, that is, PID (packet ID). The demultiplexer 22 at the receiving side demultiplexes the TSP""s corresponding to the information data 12 and 13 based on the unique PID""s assigned to the TS""s of the information data 12 and 13 at the multiplexing circuit 14 of the transmission side. The TS header also includes an error indication flag (transport error indicator). If error is included in the corresponding TSP, the error indicating flag becomes 1, while if error is not included, the error indicating flag becomes 0. The receiving side usually discards or otherwise processes a TSP including error. The data section of 184 bytes can be one of three types: a payload (FIG. 6(A)), an adaptation field (FIG. 6(B)), and a payload and adaptation field (FIG. 6(C)).
Here, while the data is demultiplexed by the demultiplexer 22 based on the PID""s, since the noise 28 is added to the transmission data 17 on the transmission line 18, if the channel-decoded data 21 includes error, the PID may have error and correct demultiplexing may not be possible. In this case, the demultiplexed data 23 corresponding to the information data 12 of the transmission side may be missing some TSP""s and this will affect the source decoding. In other words, the drawback will occur of the image or sound being disturbed or interrupted. Note that the same applies to the demultiplexed data 24 corresponding to the information data 13 of the transmission side.
To keep these drawbacks to the minimum, error control is required when transmitting data over a transmission line having error. Error control is usually performed by the error-correcting coding circuit 29 in the channel encoding circuit 16. In particular, in transmission by a transmission medium having poor conditions such as in urban areas in terrestrial transmission, mobile reception, and at boundaries of service areas, the above loss of TSP""s frequently occurs and the reliability of the data becomes a problem. For example, when a received signal is stored in a storage medium such as tape or disk for use, especially in the case of a pay service offered along with the future digitalization of communication and broadcasting, not only will the occurrence of error itself become a problem, but also the charging for error-ridden data may cause a serious problem. As a means for solving this problem, the method of making error correction more powerful etc. can be considered, but in general, if performing powerful error correction, the amount of processing for the decoding at the receiving side can be expected to also increase and the size of the receiving apparatus or the increased power consumption will become a problem. Further, in broadcasting, where real time is demanded, the delay caused by the decoding is desirably made as short as possible. Therefore, another means is desired.
The present invention has been made in consideration of the foregoing situation and has as its object is to provide a transmission system which allows highly real-time, simple decoding, while allowing error, when performing powerful error correction and which performs processing which allows a sufficient error-correcting characteristic to be achieved by performing predetermined processing. In addition, the present invention provides means for normally simply decoding the data transmitted by the above transmission system at a receiving side for viewing and listening, but, if necessary performing a predetermined error-correcting decoding to reproduce a desired piece of music with a high reliability and storing it in a storage medium.
To achieve the foregoing object, a data transmission system according to the present invention is a data transmission system for transmitting transmission data including at least one source data to a receiving side through a transmission line, comprising an encoding means for encoding the transmission data based on an error correcting coding method enabling control of the real-time characteristic and/or the error-correcting characteristic at the receiving side; a transmitting means for transmitting the transmission data encoded by said encoding means over the transmission line; a receiving means for receiving the transmission data over the transmission line; a first decoding means for decoding the data received by said receiving means by a first error correcting decoding method; a storage means for storing the data received by said receiving means; and a second decoding means for decoding the data stored by said storage means by a second error correcting decoding method.
Further, the data transmission method of the present invention is a data transmission method for transmitting transmission data including at least one source data to a receiving side through a transmission line, comprising a step of encoding the transmission data according to an encoding method enabling control of the real-time characteristic and/or error-correcting characteristic at the receiving side; a step of outputting the encoded transmission data through the transmission line; a step of receiving data through the transmission line; a step of decoding the received data by a first error correcting decoding method; a step of storing the received data; and a step of decoding the stored data by a second error correcting decoding method.
Further, the data receiving apparatus according to the present invention is a data receiving apparatus for receiving transmission data encoded by an encoding method enabling control of the real-time characteristic and/or error-correcting characteristic at the receiving side and modulated through a transmission line, comprising a demodulation means for demodulating the transmission data; a first decoding means for decoding the data demodulated by said demodulation means by a first error correcting decoding method; a first demultiplexing means for demultiplexing the data decoded by said first decoding means; a storage means for storing the data demodulated by said demodulation means; a second decoding means for decoding the data stored by said storage means by a second error correcting decoding method; and a second demultiplexing means for demultiplexing the data decoded by said second decoding means.
Further, preferably, in the present invention, the first decoding means has a higher real-time characteristic than the second decoding means.
Further, preferably, in the present invention, the second decoding means has a higher error-correcting capability than the first decoding means.
Further, preferably, in the present invention, there are further provided a reproducing means for reproducing sound and/or image signals for viewing and listening of the user from the data demultiplexed by the first demultiplexing means and a recording means for recording the data demultiplexed by the second demultiplexing means on a predetermined recording medium.